Sahih al-Bukhari 998
صحيح البخاري#998SahihNarrated `Abdullah bin `Umar:The Prophet (ﷺ) said, "Make witr as your last prayer at night
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 14:9